[1.10.x] Fixed #26644 -- Allowed wrapping NamedTemporaryFile with File.

914c72be2a introduced a regression that
causes saving a NamedTemporaryFile in a FileField to raise a
SuspiciousFileOperation. To remedy this, if a File has an absolute
path as a filename, use only the basename as the filename.

Backport of 1b407050dd from master

tests/files/tests.py

@@ -26,6 +26,12 @@ else:
 
 
 class FileTests(unittest.TestCase):
+
+    def test_file_truncates_namedtemporaryfile_name(self):
+        named_file = NamedTemporaryFile()
+        f = File(named_file)
+        self.assertEqual(f.name, os.path.basename(named_file.name))
+
     def test_unicode_uploadedfile_name(self):
         uf = UploadedFile(name='¿Cómo?', content_type='text')
         self.assertIs(type(repr(uf)), str)